Adjustable spark gap structure with preionizing means



March 31, 1970 J. c. OSTERHOUT 3,504,221

A DJUSTABLE SPARK GAP STRUCTURE WITH PREIONIZING MEANS Filed April 1, 1969 United States Patent US. Cl. 313-325 6 Claims ABSTRACT OF THE DISCLOSURE A spark gap assembly for a lightning arrester, the assembly comprising a plurality of stacked insulating plates with adjecent plates forming respectively therebetween arc chambers with a peripheral wall, a pair of electrodes disposed within each chamber and forming a spark gap near the peripheral wall, an opening in said wall and adjacent said spark gap, a piece of ionizing material inserted through said opening and disposed in said gap, and an electromagnetic coil disposed outside of the plate stack and around one of the plates for moving an arc struck in said chamber when a voltage of a predetermined magnitude in applied to the arrester.

Background of the invention The invention relates generally to lightning arresters, and particularly to an economical spark gap structure that is easy to manufacture, adjust and gauge, and is capable of handling high current surges without breakage and without excessive arc voltages.

In designing and building lightning arresters, severa factors are generally considered in the industry. These include the consistency of sparkover voltage, the level of arc voltage, arrester breakage with high current surges, the cost of the arrester and the facility with .which the arrester can be assembled and manufactured.

To improve the consistency of the sparkover voltage, preionizing means are employed in or adjacent the main spark gaps, said means providing electrons in the gap area to initiate the discharge process when a predetermined voltage level is reached across the gap.

As well known in the arrester industry, an arrester is designed to function, i.e., discharge, at a predetermined level of voltage applied across it, for example, an overvoltage of a predetermined amount on a high voltage line to which the arrester is connected. At no time should the voltage across the arrester exceed this predetermined protective level. In this manner, the arrester provides protection for electrical equipment, connected to the line, from overvoltages of predetermined amounts by discharging said voltages to ground. An excessive arc voltage in the arrester is thus undesirable because it could cause the total arrester voltage drop under certain discharge conditions to exceed the predetermined protective level.

In regard to the problem of breakage, the insulating plates in high voltage arrester gaps have heretofore cracked and broken when subjected to surges of current in the order of 100,000 amperes. The mechanical forces exerted on the gap electrodes, and thus on the supporting plate structures, are instantaneous and enormous with a current surge of such a magnitude, the forces being a result of both the heat generated by the surge and the magnetic field created by the flow of current.

The factors of cost and facility of making the arresters are predicated on the number and type of component parts that comprise the finished arrester. For example, in many arresters presently being made, it is difficult to properly gauge the spark gaps, and then fix the elec- 3,504,221 Patented Mar. 31, 1970 trodes forming the gaps in their gauged position to prevent future movement of the electrodes and a change in the gap.

In a similar manner, existing preionizer devices are both costly and difiicult to properly locate and fix in the arc chambers of the arrester.

Another item adding to cost of the arrester is the specially made insulating plate or plates designed to accommodate and support electromagnetic coils. Such coils are used to stretch the arc within the arc chamber after it is struck thereby greatly increasing the energy absorbing duty imposed upon the arrester. Specially made coil supporting plates add to the number of different components which comprise the stack assembly thereby increasing the complexity and thus the cost of the assembly process.

Brief summary of the invention The present invention provides an economical spark gap assembly for lightning arresters which is easy to assemble, easy to adjust, gauge and fix the spark gaps, and to locate and fix an ionizing means for preionizin g said gaps, has an adequate but not excessive arc voltage, and can withstand very large current surges.

These ends are accomplished by using identical insulating plates throughout the gap assembly including the end plates and the plate employed to support an electromagnetic coil. The plates are preferably made from a permeable ceramic material and support spark gap forming electrodes on opposed faces thereof. The plates are placed together to form arc chambers in the overall gap assembly, each chamber having an outer, peripheral wall. In said wall, and adjacent the gap formed by an electrode pair in each chamber, is provided an opening for receiving a feeler gauge and a relatively thin piece or slab of ionizing material after the gap is gauged and fixed. The gap is gauged by relative rotation of the insulating plates which move their respective electrodes into contact with the feeler gauge, the plates thereafter being suitably secured together. The ionizing piece, which is preferably a wedge shaped or tapered member, is inserted between the electrode with its narrow end first. When the member is stopped by wedging action between the electrodes, the wide end thereof substantially fills the opening in the peripheral wall. The member is then simply fixed in place by deposit of adhesive cement disposed in the opening and behind the member. A preformed, self-supporting coil is simply disposed about the outside of one of the insulating plates and held in place between, and electrically connected to, two terminal tabs extending radially outward from two adjacent plates respectively, the tabs being respectively connected to two electrodes forming the spark gap in a corresponding arc chamber.

The drawings The invention, with its advantages and objectives, will be more apparentfrom reading the following detailed description in connection with the accompanying drawing in which:

FIGURE 1 is an exploded perspective view of a main gap structure constructed in accordance with the principles of the invention;

FIG. 2 is a plan view of the male side of an insulating plate employed in the structure of FIG. 1;

FIG. 3 is a side elevation view (in partial section) of the plate of FIG. 2;

FIG. 4 is a plan view of the female side of the plates of FIGS. 2 and 3;

FIG. 5 is a side elevation view of a stack of insulating plates forming a spark gap assembly in accordance with the invention; and

3 FIG. 6 is a top plan view of the assembly of FIG. 5.

Preferred embodiment Specifically, FIG. 1 shows in perspective, two insulating plate structures 10 adapted to be fitted together to form I a chamber 12 in which an arc can be struck and moved in the manner explained hereinafter. The plates are identical to each other, and support spark gap electrodes 14 respectively on the opposite sides of each plate, the electrodes being attached thereto by rivets 17 extending through the plates.

The electrodes are so located on the plates that when the plates are placed together the electrodes of adjacent plates form a spark region 18 between them in the well known manner.

Each of the plates 10 has a male and female face or side, the male side of the upper plate, and the female side of the lower plate being visible in FIG. 1. The male face, as best seen in FIG. 3, has a circular, circumferentially extending raised portion or projection 19 surrounding a recessed area 20 occupying the center portion of the male face. The female side of each plate is provided with a peripheral recess 21 dimensioned to accommodate the circular projection 19 of an adjacent plate. In this manner, the plates can be placed together to form a compact spark gap assembly or stack 22 as shown in FIG. 5.

The center recessed area 20 provided in the male side of the plate 10 forms a peripheral Wall portion 23 thereabout as best seen in the sectional view of FIG. 3. Thus, when the plates are placed together, the wall 23, with the male and female faces of adjacent plates, defines the arc chamber 12, the area of the arc chamber being essentially that of the recessed area 20.

The plate 10 is further provided with an elongated slot 24 extending radially through the wall 23 adjacent the electrode 14 and through the area of the spark gap 18. If both the male and female sides of the plates are provided with such a slot, as shown in the figures, when adjacent plates are properly disposed together, the slots combine to form an opening 25 in the manner shown in the assembled stack 22 of FIG. 5. The opening 25 provides access to the spark gap 18 in each of the arc chambets formed by each pair of plates properly fitted together.

The male side of the plate 10 is further provided with a projection 28 near the edge of the plate, and between interrupted ends of the circumferentially extending projection 19. In a similar manner, the female side of the plate is provided with recess 29 located and dimensioned to accommodate the projection 28. The dimensions of the recesses are somewhat larger than those of the projections for reasons explained hereinafter.

At least two of the plates 10 are provided further with a metal tab 31 (FIG. 2) attached to the electrode 14 by the rivet 17 and extending radially therefrom to the outsideof the plate through the Wall 23. The tab may be accommodated in the wall between adjacent plates by shallow recesses 32 provided therein. In the stack assembly of FIG. 5, the two plates are designated respectively 10A and 103.

A slab or wedge or chip of ionizing material 33, for example steatite, is provided and dimensioned for disposal in each of the spark gaps 18 and in the radial slots 24. The slabs of steatite (or other suitable ionizing material) provide a preionization discharge for the spark gaps to insure proper and timely discharge of the gaps and thus proper functioning of the arrester unit (not shown) in which the gaps are employed.

A simple prewound electromagnetic coil 34 (FIG. 5) with insulating sleeves 34A is provided for the stack 22 for producing an are moving magnetic field in the arc chamber. The coil 34 is bonded to form a solid, selfsupporting structure so that a coil form for supporting the coil is not necessary. The coil has two loose lead ends 35 for respective electrical connection to the metal tabs 31 as shown in FIGS. 5 and 6. In this manner the coil is connected across the spark gap 18 associated with the metal tabs during the stack assembly process described hereinafter.

The exposed sides of the topmost and lowermost plates 10, which form the end plates for the stack assembly 22, may be provided respectively with metal contact or terminalplates 36 and 37 attached thereto and to respective spark gap electrodes, 14 by rivets 38 as shown in FIGS. 5 and 6. In this manner, the stack22 can be electrically connected in the circuit of an associated arrester unit by having other arrester components disposed in physical contact with said plates. A lanced portion 39 is provided in each metal plate (with the rivet extending therethrough) to allow the head of the rivet to lie in a plane below that of the terminal plate.

The structure, as thus far described, provides an easily assembled economical spark gap assembly (for example, 22 in. FIGS. 5 and 6) having an adjustable gap feature providing a simple method of gauging each gap, and simple means for fixing and providing preionization for each gap after it is gauged. I

The assembly 22 is assembled and the spark gaps 18 therein are adjusted and fixed in the following manner. Firstly, the lowermost end plate 10, with the terminal plate 37 on its male side, is clamped or otherwise fixedin a chuck or other suitable clamping device with the female side of the plate facing in an upward direction. A relatively small amount of soft but hardenable adhesive element (represented by numeral 40 in FIG. 5) is next deposited in the recess 29, and a next plate 10C disposed in mating relation with the plate secured in the chuck. In this manner, the projection 28 on the male side of the plate 10C is disposed to seat in the soft cement deposited in the recess 29 of the lowermost plate. The recesses 29 and the projections 28 are located in the plate faces in a manner to effect proper location of the electrodes 14 for forming the spark gaps 18, and the proper location of the slots 24 for forming the openings 25 in the walls of each chamber 12.

The spark gap 18 is next gauged by simply inserting a feeler gauge (not shown) into the opening 25 and into the gap and rotating the one plate relative to its neighbor or adjacent plate 'until the electrodes engage the feeler gauge. Additional plates (including 10A and 10B having tabs 31) are stacked and their spark gaps gauged in the manner described. After the gauging of the gaps is completed, the cement is allowed to set or harden thereby fixing the gaps in their gauged position.

After the position of the plates is fixed in the manner described, the wedge or tapered piece of ionizing material 33 p is inserted, with the narrow end forward, radially through the opening 25 and into the spark gap 18 between the electrodes 14. The wedge is moved inwardly until it is stopped by wedging between the electrodes. The wedge is secured in position by a small quantity (not shown) of adhesive cement deposited in the opening behind the exposed end of the wedge. All of the spark gaps 18 are provided with the wedge in the manner described.

Before the plate 10A is diposed on 108, however, the prewound coil 34 is pressed over and disposed about the plate so that the coil will lie between the tabs 31 attached to the plates, as seen in FIG. 5, when 10A is disposed on 10B. Thereafter, plates are added to complete the stack, and the spark gaps formed thereby are gauged, fixed and provided with ionizing wedges in the manner described above.

The lead ends 35 of the coil 34 are suitably electrically connected to the metal tabs 31 on the two plates 10A and 10B, and thereby electrically connected across the spark gap formed by the adjacently disposed electrodes of the two plates. In this manner, when an arc is struck between the electrodes, a portion of the arc current is transferred to the coil which instantly develops a magnetic field in the arc chambers 12 to spread the are out and away from its point of origin between the electrodes in the well known manner.

As shown in FIGS. 5 and 6, the insulating sleeves 34A are disposed adjacent the connections of the coil leads 35 and the metal tabs 31 to insure insulation of the coil body from the metal tabs.

The number (seven) of insulating plates 10 shown in the assembly 22 of FIG. 5 is given by way of example only, the actual number of plates and are chambers 12 being chosen in accordance with the requirements of the line or circuit in which the complete arrester will be employed.

The spark gap assembly as herein disclosed has the above described required sparkover characteristics, name- 1y, a consistent sparkover voltage provided by the simply disposed ionizing wedge 33, an adequate, but not excessive arc voltage, a gap plate assembly that can handle large ampere surges without breaking at a cost of about onehalf /2) that of former designs, and it is easy to manufacture and assemble since all of the insulating plates 10 are identical and a minimum of separate parts and items are required. In comparison to a conventional gap assembly for a similarly rated station type arrester, the gap assembly of the present invention has approximately onehalf /2) as many parts.

The present invention further provides a gap structure that is easily adjustable, thereby overcoming prior manufacturing problems experienced with gaugable spark gaps.

Though the invention has been described with a certain degree of particularity, it should be understood that changes may be made therein without departing from the spirit and scope thereof.

What is claimed is:

1. A spark gap assembly comprising a stack of identical insulating plates, each two of said plates forming therebetween a chamber with a pcripheral wall for containing an arc struck in said chamber,

each of said chambers having mounted therein a pair of electrodes forming a spark gap therebetween and near the peripheral wall of each chamber, said pair of electrodes comprising an electrode supported respectively on opposite faces of each plate,

each of said plates having a slot adjacent at least one of its electrodes, and extending radially past said electrode and through the peripheral wall of each chamber to form an opening therein,

a piece of ionizing material radially inserted through said opening and radially disposed in said slot and between the pair of electrodes forming said spark gap, and

an electromagnetic coil physically disposed about the outside of at least one of said plates in said stack and electrically connected across one of said spark gaps, said coil being a bonded, self-supporting unit.

2. The assembly described in claim 1 in which the piece of ionizing material has a tapered configuration.

3. The assembly described in claim 1 in which the material of the ionizing piece is steatite.

4. The assembly described in claim 1 in which the piece of ionizing material is fixed in place in the spark gap by cement disposed in the opening formed by the radially extending slot.

5. The assembly described in claim 1 in which the spark gap is fixed by a deposit of cement located between the faces of adjacent plates.

6. The assembly described in claim 1 in which the insulating plates are made from a porous ceramic material.

References Cited UNITED STATES PATENTS 3,069,589 12/ 1962 Cunningham 315-36 3,353,059 11/1967 Buffa et al 31536 3,366,825 1/1968 Lafierty 313-217 3,378,722 4/ 1968 Osterhout et al. 315-36 JAMES D. KALLAM, Primary Examiner SIMON BRODER, Assistant Examiner US. 01. X.R. 31 3-243, 315-6, 

